Circulating tumor markers are being studied to aid in detection and diagnosis and monitoring the course of patients with various neoplastic diseases. Sensitive quantitation of alpha-fetoprotein (AFP) by radioimmunoassay has been shown to be of considerable value for following therapy in patients with hepatocellular carcinoma (HC) and testicular cancer of germ cell origin where quantitation of human chorionic gonadotropin (HCG) also serves as an indicator of tumor activity. Experimental studies in primates with chemically induced HC allow the demonstration of the usefulness of AFP for early detection of tumor and also to calculate the synthetic rate and catabolic rate of AFP to estimate the total body tumor load. Similar studies are being started with patients having testicular germ cell tumors. A new human lung tumor-associated antigen (LTAA) has been isolated and characterized. The labeled antigen is being used to set up a sensitive RIA for the quantitation of LTAA levels in sera of patients with lung cancer and other disease conditions. Similar studies are being performed using a murine virus-induced leukemia (MBL-2) as a model system and quantitating tumor-associated antigen(s) by an antibody- and complement-mediated cytotoxicity (51Cr release) assay. BIBLIOGRAPHIC REFERENCES: Waldmann, T.A., McIntire, K.R., Adamson, R.H. and Dalgard, D.W.: The metabolism of tumor related proteins. In Bianchi, R., Mariani, G., and McFarlane, A.S. (Eds.): Plasma Protein Turnover. London, McMillan, 1976, pp. 155-165. McIntire, K.R., Vogel, C.L., Primack, A., Waldmann, T.A. and Kyalwazi, S.K.: Effect of surgical and chemotherapeutic treatment on alpha-fetoprotein levels in patients with hepatocellular carcinoma. Cancer 37: 677-683, 1976.